Thermal Performance Enhancement of L-Shaped Microgrooved Heat Pipe Containing Water-Based Al2O3 Nanofluids

An experimental study was performed to investigate the thermal performance of an L-shaped grooved heat pipe with cylindrical cross section, which contained 0.5 wt% water-based Al₂O₃ nanofluid as the working fluid. The transient performance of the heat pipe and the effect of cooling water temperature on the heat transfer characteristics of the heat pipe were investigated. The outer diameter and the length of the heat pipe were 6 mm and 220 mm, respectively. Experimental results revealed that the temperature of the cooling water has a significant effect on the thermal resistance of the heat pipe containing nanofluids as its working fluid. By increasing the cooling water temperature from 5°C to 27.5°C, the thermal resistance decreases by approximately 40%. At the same charge volume, test results indicated an average reduction of 30% in thermal resistance of heat pipes with nanofluid as compared with heat pipe containing pure water. For transient conditions, unsteady state time for nanofluids was reduced by approximately 28%, when compared with water as the working fluid.     

CFD analysis of a flat tube with semi-circular fins using graphene nanofluid and to compare performance with square type of fins

CFD analysis on a flat tube with semi-circular fins under laminar flow conditions was performed with graphene-based nanofluids considering the nanofluids as incompressible. Different simulations were performed at four different concentrations of nanofluids (0.01%, 0.1%, 0.2%, and 0.4%) and at different volume flow rates (4, 6, 8, and 10 LPM) and at four different forced convective heat transfer coefficients at different wind velocities at 300 K (50, 100, 150, and 200 W/m² K). It was observed that with an increase in the concentration of nanoparticles in nanofluids, the thermal conductivity of base fluid water was increased (at 353 K the nanofluid of 0.4% volume concentration, the thermal conductivity of nanofluid increased by 200% with respect to base fluid). Graphene-based nanofluids have higher effectiveness than most nanofluids hence it is considered for the analysis, at 0.4% concentration of nanofluid the effectiveness observed was 36.84% at 4 LPM, and for water, the effectiveness was 28.22% under similar conditions. The effect of flow rate on temperature drop was significant. At 4 LPM and at 0.4% of nanofluid, an outlet coolant temperature of 333 K was observed whereas the water outlet temperature at 10 LPM is 346.13 K. The effect of forced convective air heat transfer coefficient was significantly high. At h = 50 W/m² K the outlet temperature of 0.4% nanofluid at 4 LPM was 345.25 K and at h = 200 W/m² K, the outlet coolant temperature was 333.47 K. A single tube of the radiator was considered for the analysis whereas the original radiator consists of 50 tubes due to problems of Ansys in meshing.     

Heat Transfer Performance of Heat Pipe Radiator with SiO2/Water Nanofluids

The effect of nanofluids on thermal performance of the miniature heat pipe radiator which was assembled by two heat pipes containing 0.6 vol.% SiO₂/water nanofluids and 30 pieces of rectangular aluminum fins was investigated experimentally and theoretically. The wall temperatures of the miniature heat pipe and fin surface temperatures were measured. Results showed that the utilization of SiO₂/water nanofluids as a working fluid in the heat pipe enhanced the heat performance by reducing wall temperature differences. Compared with Deionized water (DI water), the thermal resistance of the miniature heat pipe with SiO₂/water nanofluids decreased by about 23% to 40%. Furthermore, the theoretical calculation on a basis of one dimension found that the fin heat dissipation in the miniature heat pipe radiator charged SiO₂/water nanofluids was about 1.17 times of that of the DI water radiator.     

Numerical and Experimental Investigation of Heat Transfer of α-Al2O3/Water Nanofluid in Double Pipe and Shell and Tube Heat Exchangers

This research presents an experimental and numerical study on the heat transfer of α-Al₂O₃/water nanofluid flowing through the double pipe and shell and tube heat exchangers, under laminar flow conditions. Effects of important parameters such as hot and cold volume flow rates, nanofluid temperature, and nanoparticles concentration on the heat transfer characteristics are investigated. The results indicated that the heat transfer performance of both double pipe and shell and tube heat exchangers increases with increasing the hot and cold volume flow rates, as well as the particle concentrations and nanofluid inlet temperature. Compared with pure water, the results indicated that the heat transfer coefficients of nanofluid in the double pipe and shell and tube heat exchangers are higher than those of water by 13.2% and 21.3%, respectively. Also, the heat transfer performance of nanofluid in a shell and tube heat exchanger is 26.2% higher than the double pipe heat exchanger. A computational fluid dynamics (CFD) technique was used for heat transfer simulation in the previously mentioned heat exchangers. Computed overall heat transfer coefficients of the nanofluids are in good agreement with the experimental data.     

Experimental and analytical investigation on an automobile radiator with CuO/EG‐water based nanofluid as coolant

In the present study, experimental and analytical thermal performance of automobile radiator using nanofluids is investigated and compared with performance obtained with conventional coolants. Effect of operating parameters and nanoparticle concentration on heat transfer rate are studied for water as well as CuO/EG‐water based nanofluid analytically. The results are presented in the form of graphs showing variations of net heat transfer rate for various coolant flow rate, air velocity, and source temperature for various CuO/EG‐water based nanofluids. Experimental results indicate that with the increase in coolant flow rate and air velocity, heat transfer rate increases, reaches maximum and then decreases. Experimental investigation of a radiator is carried out using CuO/EG‐water based nanofluids. Results obtained by experimental work and analytical MATLAB code are almost the same. Maximum absolute error in water and air side is within 12% for all flow condition and coolant fluids. Nusselt number of nanofluid is calculated using equation number 33[9]. The results obtained from experimental work using 0.2% volume CuO/EG‐water based nanofluids are compared with the results obtained from MATLAB code. The results show that the maximum error in the outlet temperature of the coolant and air is 12% in each case. Thus MATLAB code can be used for different concentration of nanofluids to study the effect of operating parameters on heat transfer rate. Thus MATLAB code developed is valid for given heat exchanger applications. From the results obtained by already validated MATLAB code, it is concluded that increase in coolant flow rate, air velocity, and source temperature increases the heat transfer rate. Addition of nanoparticles in the base fluid increases the heat transfer rate for all kind of base fluids. Among all the nanofluid analyzed in this study, water‐based nanofluid gives highest value of heat transfer rate and is recommended for the heat exchanger applications under normal operating conditions. Maximum enhancement is observed for ethylene glycol‐water (4:6) mixture for 1% volume concentration of CuO is almost equal to 20%. As heat transfer rate increases with the use of nanofluids, the heat transfer area of the radiator can be minimized.     

Thermal performance of flat-shaped heat pipes using nanofluids

Analytical models are utilized to investigate the thermal performance of rectangular and disk-shaped heat pipes using nanofluids. The liquid pressure, liquid velocity profile, temperature distribution of the heat pipe wall, temperature gradient along the heat pipe, thermal resistance and maximum heat load are obtained for the flat-shaped heat pipes utilizing a nanofluid as the working fluid. The flat-shaped heat pipe’s thermal performance using a nanofluid is substantially enhanced compared with one using a regular fluid. The nanoparticles presence within the working fluid results in a decrease in the thermal resistance and an increase in the maximum heat load capacity of the flat-shaped heat pipe. The existence of an optimum nanoparticle concentration level and wick thickness in maximizing the heat removal capability of the flat-shaped heat pipe was established.     

Effect of nanofluids on the thermal performance of a flat micro heat pipe with a rectangular grooved wick

In this paper, the effect of water-based Al₂O₃ nanofluids as working fluid on the thermal performance of a flat micro-heat pipe with a rectangular grooved wick is investigated. For the purpose, the axial variations of the wall temperature, the evaporation and condensation rates are considered by solving the one-dimensional conduction equation for the wall and the augmented Young–Laplace equation for the phase change process. In particular, the thermophysical properties of nanofluids as well as the surface characteristics formed by nanoparticles such as a thin porous coating are considered. From the comparison of the thermal performance using both DI water and nanofluids, it is found that the thin porous coating layer formed by nanoparticles suspended in nanofluids is a key effect of the heat transfer enhancement for the heat pipe using nanofluids. Also, the effects of the volume fraction and the size of nanoparticles on the thermal performance are studied. The results shows the feasibility of enhancing the thermal performance up to 100% although water-based Al₂O₃ nanofluids with the concentration less than 1.0% is used as working fluid. Finally, it is shown that the thermal resistance of the nanofluid heat pipe tends to decrease with increasing the nanoparticle size, which corresponds to the previous experimental results.     

Experimental comparative study of heat pipe performance using CuO and TiO2 nanofluids

In recent years, developing an energy efficient conventional heat pipe is more important because of the development of electronics and computer industries. To enhance the thermal performance of heat pipe, different nanofluids have been widely used. In this paper, an experimental investigation of heat transfer performance of heat pipe has been conducted using three different working fluids such as DI water, CuO nanofluid and TiO₂ nanofluid. The heat pipe used in this study is made up of copper layered with two layers of screen mesh wick for better capillary action. The Parameters considered in this study are heat input, angle of inclination and evaporator fill ratio. The concentration of nanoparticle used in this study is of 1.0 wt.%. From the experimental results, comparisons of thermal performance were made between the heat pipes using various working fluids. Among various fill ratio charged, the heat pipe shows good thermal performance when it is operated at 75% fill ratio for all working fluids. However, the heat pipe operated with CuO nanofluid showed higher results compared with TiO₂ nanofluid and DI water. Copyright © 2013 John Wiley & Sons, Ltd.     

水基纳米流体在铜丝平板热管中的应用

对使用三种水基纳米流体作为工质的铜丝平板热管的传热特性进行了实验研究.使用的纳米流体分别是平均粒径20 nm的Cu纳米颗粒、平均粒径50 nm的Cu纳米颗粒和平均粒径50 nm的CuO纳米颗粒的水基悬浮液(简称水基20 nm Cu、50 nm Cu、50 nm CuO纳米流体),着重分析了纳米流体种类,纳米颗粒质量分数、运行温度或工作压力对热管传热特性的影响.研究结果表明,使用纳米流体作为工质可以显著提高热管的传热特性;在不同运行温度条件下,不同的纳米流体均在质量分数1.0％时具有最佳传热效果;纳米流体是一种适用于铜丝平板热管的新型工质.     

The impact of various nanofluid types on triangular microchannels heat sink cooling performance

This paper discusses the impact of using various types of nanofluids on heat transfer and fluid flow characteristics in triangular shaped microchannel heat sink (MCHS). In this study, an aluminum MCHS performance is examined using water as a base fluid with different types of nanofluids such as Al₂O₃, Ag, CuO, diamond, SiO₂, and TiO₂ as the coolants with nanoparticle volume fraction of 2%. The three-dimensional steady, laminar flow and heat transfer governing equations are solved using the finite volume method. It is inferred that diamond-H₂O nanofluid has the lowest temperature and the highest heat transfer coefficient, while Al₂O₃-H₂O nanofluid has the highest temperature and the lowest heat transfer coefficient. SiO₂-H₂O nanofluid has the highest pressure drop and wall shear stress while Ag-H₂O nanofluid has the lowest pressure drop and wall shear stress among other nanofluid types. Based on the presented results, diamond-H₂O and Ag-H₂O nanofluids are recommended to achieve overall heat transfer enhancement and low pressure drop, respectively, compared with pure water.     

Thermal performance of screen mesh wick heat pipes using water-based copper nanofluids

Fairly stable surfactant free copper–distilled water nanofluids are prepared using prolonged sonication and homogenization. Thermal conductivity of the prepared nanofluid displays a maximum enhancement of ～15% for 0.5 wt% of Cu loading in distilled water at 30 °C. The wall temperature distributions and the thermal resistances between the evaporator and the condenser sections of a commercial screen mesh wick heat pipe containing nanofluids are investigated for three different angular position of the heat pipe. The results are compared with those for the same heat pipe with water as the working fluid. The wall temperatures of the heat pipes decrease along the test section from the evaporator section to the condenser section and increase with input power. The average evaporator wall temperatures of the heat pipe with nanofluids are much lower than those of the heat pipe with distilled water. The thermal resistance of the heat pipe using both distilled water and nanofluids is high at low heat loads and reduces rapidly to a minimum value as the applied heat load is increased. The thermal resistance of the vertically mounted heat pipe with 0.5 wt% of Cu–distilled water nanofluid is reduced by ～27%. The observed enhanced thermal performance is explained in light of the deposited Cu layer on the screen mesh wick in the evaporator section of the heat pipe.     

Analysis and thermal response test for vertical ground heat exchanger with two U‐loop configuration

An in situ thermal response test (TRT) is applied to evaluate the thermal performance of the vertical ground heat exchanger (GHX) with two U‐loop configuration. A line source method is used to derive the thermal conductivity and borehole thermal resistance from the measured data. Analyses are made to improve the interpretation of TRT data and to investigate the active area of interest in the borehole. Load tests of the GHX are performed to examine the daily variations of ground and mean fluid temperatures associated with daily intermittent operation of ground source heat pump system. Results show that while the ground thermal conductivity of two U‐loop GHX is moderately increased, the borehole thermal resistance is significantly reduced, compared with the single U‐loop GHX. Of the borehole thermal resistance components evaluated, the grout thermal resistance is the most governing one in the borehole heat transfer (77% of the total borehole thermal resistance), whereas the convective thermal resistance in the tube is almost negligible (less than 2%). Copyright © 2015 John Wiley & Sons, Ltd.     

Thermal performance enhancement studies using graphite nanofluid for heat transfer applications

Enhanced boiling heat transfer using nanofluids is highly relevant due to its potential applications in thermal management of systems producing large heat fluxes. However, the sedimentation of nanoparticles limits their application in heat transfer systems. So, the preparation of a stable nanofluid remains a big research challenge. The stability issues arise due to the large difference in the density of nanoparticle and the base fluid. Graphite nanoparticle is selected in this study, as it has 4.5 times lower density than copper and comparable thermal conductivity. An experimental study is conducted to evaluate the suitability of graphite nanofluid in mesh wick heat pipes, which are devices that utilize boiling and condensation principles to transfer high heat fluxes. Thermal transport properties and boiling heat transfer characteristics showed enhancement and the effect of nanofluid on the device level thermal performance is thoroughly assessed. Experimental results are compared with the published literature. A reduction in thermal resistance by 32.5% and an improvement in the heat transfer coefficient by 48.02% in comparison with base fluid clearly indicate the superiority of the graphite nanofluid for heat transfer applications.     

Ground heat exchanger temperature distribution analysis and experimental verification

The underground two-dimensional symmetry temperature field of a vertical double spiral coil ground heat exchanger (GHX) designed by the authors for a ground source heat pump (GSHP) system was simulated using the volume-control method. A heat transfer model of underground coil is made, and the underground temperature distribution of the coil was solved numerically. Experimental temperature data are measured. The analytical results are compared thoroughly with the experimental data. The mathematical mode presented herein may provide design guidance for the design of GHX for GSHP systems.     

An investigation of the thermal performance of cylindrical heat pipes using nanofluids

In this work, a two-dimensional analysis is used to study the thermal performance of a cylindrical heat pipe utilizing nanofluids. Three of the most common nanoparticles, namely Al₂O₃, CuO, and TiO₂ are considered as the working fluid. A substantial change in the heat pipe thermal resistance, temperature distribution, and maximum capillary heat transfer of the heat pipe is observed when using a nanofluid. The nanoparticles within the liquid enhance the thermal performance of the heat pipe by reducing the thermal resistance while enhancing the maximum heat load it can carry. The existence of an optimum mass concentration for nanoparticles in maximizing the heat transfer limit is established. The effect of particle size on the thermal performance of the heat pipe is also investigated. It is found that smaller particles have a more pronounced effect on the temperature gradient along the heat pipe.     

Experimental performance evaluation of a closed‐loop vertical ground source heat pump in the heating mode using energy analysis method

An experimental study is performed to determine the performance of a ground source heat pump (GSHP) system in the heating mode in the city of Erzurum, Turkey. The GSHP system using R‐134a as refrigerant has a single U‐tube ground heat exchanger (GHE) made of polyethylene pipe with a 16 mm inside diameter. The GHE was placed in a vertical borehole with 55 m depth and 203.2 mm diameter. The average coefficients of performance (COP) of the GSHP system and heat pump in heating mode are calculated as 2.09 and 2.57, respectively. The heat extraction rate per meter of the borehole is determined as 33.60 W m^?1. Considering the current gas and electric prices in Erzurum city, the equivalent COP of the GSHP system should be 2.92 for the same energy cost comparing with natural gas. The virgin ground in Erzurum basin has high permeability and low thermal conductivity. In order to improve the thermal efficiency of GHE and thus improve COP of a GSHP in the basin, the borehole should be backfilled with sand as low‐cost backfill material and a 1 to 2 m thick surface plug of clay should be inserted. Copyright © 2007 John Wiley & Sons, Ltd.     

Counterflow HE analysis of Cu and SiO2 nanofluids in the developing flow region

Three concentrations of 0.2, 0.6, and 1.0 vol.% Copper/25 nm and silica/22 nm nanofluids are prepared in a base liquid glycerol–water mixture of 30:70 ratio by volume (GW70). The thermophysical properties of Cu and SiO₂ nanofluids are determined with a TPS500S hot disc thermal analyzer and Brookfield viscometer in the temperature range of 20–80°C. The maximum enhancement in Cu and SiO₂ nanofluid viscosity (63.4%, 35.7%), thermal conductivity (100.4%, 71.3%), and density (7.5%, 1.5%) while specific heat (7.8%, 2.3%) determined for 1.0% concentration at 80°C compared to base liquid GW70. Heat transfer experiments are conducted in a short-length double pipe heat exchanger. The flow rates resulted in the lamifnar entry length region. A maximum enhancement in the overall heat transfer coefficient (HTC; 25.0%, 19.7%) and convective HTC (46.2%, 34.8%), respectively for Cu and SiO₂ nanofluids is estimated at 1.0% concentration compared to base liquid at a bulk temperature of 35°C.     

Heat transfer enhancement with the use of nanofluids in radial flow cooling systems considering temperature-dependent properties

Heat transfer enhancement capabilities of coolants with suspended metallic nanoparticles inside typical radial flow cooling systems are numerically investigated in this paper. The laminar forced convection flow of these nanofluids between two coaxial and parallel disks with central axial injection has been considered using temperature dependent nanofluid properties. Results clearly indicate that considerable heat transfer benefits are possible with the use of these fluid/solid particle mixtures. For example, a Water/Al₂O₃ nanofluid with a volume fraction of nanoparticles as low as 4% can produce a 25% increase in the average wall heat transfer coefficient when compared to the base fluid alone (i.e., water). Furthermore, results show that considerable differences are found when using constant property nanofluids (temperature independent) versus nanofluids with temperature dependent properties. The use of temperature-dependent properties make for greater heat transfer predictions with corresponding decreases in wall shear stresses when compared to predictions using constant properties. With an increase in wall heat flux, it was found that the average heat transfer coefficient increases whilst the wall shear stress decreases for cases using temperature-dependent nanofluid properties.     

Numerical Investigation on Conjugate Heat Transfer Performance of Microchannel Using Sphericity-Based Gold and Carbon Nanoparticles

Numerical study has been carried out on the laminar forced convection flow of nanofluids in a wide rectangular microchannel. The flow and heat transfer characteristics of gold and of single-walled carbon (SWCNT) nanofluids are investigated in order to find an efficient and cost-effective heat transfer fluid. The effects of nanoparticle volume concentration and of spherical and cylindrical particulate sizes on the conjugate heat transfer performance of the microchannel are reported. The effective thermal conductivity of a nanofluid is evaluated on the basis of particle sphericity by considering the volume and surface area of the nanoparticles. The average convective heat transfer coefficient increases with increase in Reynolds number and volume concentration. Moreover, sphericity-based thermal conductivity evaluation showed that increasing the length of the SWCNT nanoparticle has significant effect on the heat transfer performance, concluding that axial heat conduction dominates the radial heat conduction within the nanoparticle. The carbon nanofluid is identified as an optimized heat transfer fluid with better heat transfer characteristics in comparison with the gold nanofluid. It also reduces the cost of the working fluid. The variations in the interface temperature between solid and fluid regions are reported for nanofluids with different concentrations at different Reynolds numbers. The diameter and length of the SWCNT nanoparticle show a significant effect on heat transfer characteristics.     

Nanofluids with encapsulated tin nanoparticles for advanced heat transfer and thermal energy storage

Novel high‐temperature heat transfer fluids (HTFs) with incorporated phase change nanomaterials were synthesized and tested for heat transfer and thermal energy storage. The advanced thermal properties were achieved by preparing a nanofluid consisting of core/shell silica encapsulated tin (Sn/SiO₂) nanoparticles dispersed in a synthetic HTF Therminol 66 (TH66) at loadings up to 5 vol%. Tin nanoparticles were synthesized by modified polyole reduction method followed by sol–gel silica encapsulation process. The measured increase in thermal conductivity of the nanofluid (~13% at 5 vol%) was in agreement with Maxwell's effective medium theory. Latent heat of phase change during melting of Sn core added ~11% increase to the volumetric thermal energy storage of the nanofluid when cycled in between 100°C and 270°C. The value could be further improved if thermal cycling is conducted in a narrower temperature range. The experimental results demonstrated dual functionality of the engineered nanofluids as desired for Concentrated Solar Power systems. Viscosity and stability of the nanofluids as well as thermal stability of core/shell nanomaterials) were investigated in a wide temperature range to obtain a perspective on any additional pumping power requirements for the nanofluid over the base fluid. Copyright © 2013 John Wiley & Sons, Ltd.